fix: Only inform if no extractor finds valid files

Until now whenever an extractor could not find any valid files for a
document it would inform the user of this case. However, this is not
very useful: if you have a pdf and an epub extractor running, it would
inform you for each document which only had one of the two formats as
well as those which actually did not have any valid files for *any* of
the extractors running.

This commit changes the behavior to only inform the user when none of
the running extractors find a valid file, since that is the actual case
a user might want to be informed about.

papis_extract/__init__.py

@@ -1,3 +1,4 @@
+import re
 import click
 import papis.cli
 import papis.config
@@ -145,10 +146,18 @@ def run(
     doc_annots: list[tuple[Document, list[Annotation]]] = []
     for doc in documents:
         annotations: list[Annotation] = []
+        valid_files: int = 0
         for ext in extractors:
             if not ext:
                 continue
-            annotations.extend(extraction.start(ext, doc))
+            added = extraction.start(ext, doc)
+            if added is not None:
+                valid_files += 1
+                annotations.extend(added)
         doc_annots.append((doc, annotations))
 
+        if valid_files == 0:
+            # have to remove curlys or papis logger gets upset
+            desc = re.sub("[{}]", "", papis.document.describe(doc))
+            logger.info(f"Document {desc} has no valid extractors for any of its files.")
     exporter.run(doc_annots)